This invention relates to voltage converter circuits and more particularly to a frequency to voltage converter circuit suitable to be fabricated in monolithic integrated circuit form to provide an analog output voltage the magnitude of which is representative of the frequency of an input signal applied thereto.
In control circuits, a control voltage proportional to the frequency of an input signal may be required. For example, a particular control system which can be contemplated is a fuel metering system for use in tomorrows automobiles. The fuel metering system would be responsive to engine speed for adjusting the fuel to air mixture ratio which is injected into the cylinders of the automobile for engine combustion. In such a system a signal having a frequency corresponding to the engine speed can be developed from which analog voltages are produced. These analog voltages may then be used to vary the air/fuel mixture ratio to ensure proper engine operation.
It is important that the frequency to voltage converter utilized in such fuel metering systems be responsive to instantaneous changes in engine rpm due to acceleration and deceleration of the automobile. Hence, the output analog voltage of the converter system should be made to be responsive to engine speed variations within one cycle of the frequency change in the applied input signal to the converter. However, typical capacitive charging and discharging systems used in the past to convert frequency signals to voltage related signals have often had too lengthly response times so as to be operable in fuel metering systems. Therefore, a need exists to provide a frequency to voltage converter having fast response times to changes in the frequency of an applied input signal such as to be suitable to be incorporated into a fuel metering system if desired.